Effluent gases output from processes such as process chambers for processing semiconductors require treatment to reduce the amount of undesirable chemicals output. For example, the semiconductor manufacturing industry may output residual perfluorinated compounds (PFCs) and other dangerous process gases such as NH3 and NF3 in the effluent gas stream pumped from the process tool. These chemicals may be difficult to remove from the effluent gas and their release into the environment is undesirable because they may be noxious and/or have relatively high greenhouse activity. Thus, treatment or abatement apparatus are required to reduce these undesirable chemicals from being output.
Known treatment apparatus use combustion to remove the undesirable compounds from the effluent gas stream. It is desirable to improve the combustion and abatement efficiency not only to increase the removal of dangerous process gases such as NH3 and NF3 but also to reduce the emissions of combustion by-products (e.g. CO, HC and NOx).
In many such combustion chambers a mixture of fuel and air are supplied to the burner to generate a flame and secondary combustion air is added to the combustion chamber. However, adding this secondary combustion air downstream of the burner head can disrupt the flame structure on the burner head and quench the temperature of the combustion chamber shortly after the process gas has passed the burner head limiting the useful residence time of the process gas in the high temperature zone. This disruption of the flame leads to combustion of particle forming process gas (e.g. Silane) in close proximity to the burner head resulting in deposition of Silica on the head and importantly in process inlet nozzles. The disruption of the flame structure also allows process gas to bypass the flame so that emissions of process gases such as Nitrogen Trifluoride are higher than necessary. The premature quenching of the flame also leads to higher than necessary emissions of Carbon Monoxide and unburnt Hydrocarbons.
The premature quenching of the combustion zone has a supplementary effect when the abatement of Ammonia is considered. Currently a substantial flow of Hydrogen gas has to be added to a stream of Ammonia process gas to ensure that the combustion chamber temperature and high temperature zone length are sufficient to allow the thermal decomposition of all the Ammonia into Nitrogen and Hydrogen and subsequent combustion of the Hydrogen. Combustion of Nitrogen containing species such as Nitrogen Trifluoride or Ammonia can lead to the formation of significant quantities of Nitrogen Oxides via the Fuel-NOx mechanism. Environmental regulation requires that these emissions be reduced. One way of doing this may be to use depleted oxygen air in the combustion chamber and this can be provided by recirculating the exhaust gas, however, this again can lead to undue turbulence with the associated problems outlined above.
It would be desirable to provide a good mixture of flame and incoming gases without generating undue turbulence which may lead to particulates formed during the combustion process not being exhausted but fouling parts of the combustion chamber such as the burner heads. It would also be desirable to provide efficient combustion while limiting the amount of NOx compounds that are exhausted.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.